1. Field of the Invention
The present invention relates to a fuel injection valve.
2. Description of Related Art
JP-B2-4243610 discloses a fuel injection valve.
The fuel injection valve has a needle valve to reciprocate in a body, a movable core, an electromagnetic actuator to attract the movable core, and a biasing portion to bias the movable core and the needle valve. The needle valve has a bar shape, and opens/closes an injection hole. The movable core has a cylinder shape, and an inner face of the movable core supports an outer face of the needle valve in a manner that the movable core is movable relative to the needle valve.
Fuel injection from the injection hole is prohibited if the needle valve is seated on a seat portion in a seating direction. Fuel injection from the injection hole is allowed if the needle valve is separated from the seat portion in a separating direction.
The movable core has a column-shaped main part and a based cylinder-shaped sleeve having the same axis as the main part. Each of the main part and the sleeve has a through hole to which a shaft of the needle valve is inserted at a center position in a radial direction. The shaft of the needle valve has two flanges protruding outward in the radial direction from outer circumference face. The two flanges are arranged in an axis direction in distanced state. One of the flanges is a first flange located opposite from the sleeve. When the first flange contacts the main part, the movable core is restricted from moving in the separating direction relative to the needle valve. The other flange is a second flange located on an inner circumference side of the sleeve, and is located between an end face of the main part adjacent to the sleeve and an inner bottom face of the sleeve.
The biasing portion has a first elastic member and a second elastic member. The first elastic member contacts the first flange, and biases the needle valve in the seating direction. The second elastic member is located between the second flange and the inner bottom face of the sleeve. The second elastic member biases the movable core in the seating direction in a state that the needle valve is seated on the seat portion. The body of the fuel injection valve has a stopper to stop a movement of the movable core in the seating direction. When electricity is not supplied to the electromagnetic actuator, magnetic attraction force is not generated, and the movable core is pressed to the stopper by the second elastic member. The movable core is held to be distanced from the first flange.
The electromagnetic actuator is located adjacent to the movable core opposite from the stopper. When the movable core is contact with the stopper, a distance between the movable core and the electromagnetic actuator is larger than a distance between the movable core and the first flange.
Therefore, the movable core can move solely until the movable core contacts the first flange, when magnetic attraction force is generated. If the movable core contacts the first flange, the movable core cannot move in the separating direction relative to the needle valve, so that the needle valve moves in the separating direction together with the movable core. Thereby, the needle valve is separated from the seat portion so as to connect a fuel passage to the injection hole, and fuel supplied from the fuel passage is injected from the injection hole.
In a conventional fuel injection valve to be driven by electromagnetic force, relative movement is prohibited between a movable core and a needle valve. In this case, when magnetic attraction force generated by an actuator is applied to the movable core, the movable core is attracted to the actuator, and the needle valve is moved in the separating direction. When the needle valve is moved in the separating direction, the magnetic attraction force is applied to the needle valve through the movable core.
In contrast, relative movement is allowed between the movable core and the needle valve in the fuel injection valve of JP-B2-4243610. Therefore, when the movable core is engaged with the needle valve and when the needle valve is separated from the seat portion, not only the magnetic attraction force but also a momentum force of the movable core are applied to the needle valve. Thus, moving speed of the needle valve in the separating direction becomes higher compared with the conventional fuel injection valve.
If fuel is supplied to the injection hole from the fuel passage through a clearance generated between the seat portion and the needle valve opposing to the seat portion, the clearance is so small immediately after the needle valve begins separating from the seat portion. At this time, a pressure of fuel flowing into the injection hole is very low. As the clearance becomes larger, the pressure of fuel flowing into the injection hole gradually becomes higher. When the clearance is so small, that is immediately after the needle valve begins separating from the seat portion, sufficient fuel cannot be supplied to the injection hole. If sufficient fuel is not supplied to the injection hole, the pressure of fuel flowing into the injection hole is low. At this time, a speed of fuel injected from the injection hole is slow, and a particle diameter of fuel injected from the injection hole becomes large, compared with a case where the needle valve is located at the farthest position from the seat portion. The particle diameter of fuel is large for a long time if the moving speed of the needle valve is slow in the separating direction.
Compared with the conventional fuel injection valve, the moving speed of the needle valve in the separating direction is made higher in JP-B2-4243610, so that a ratio of fuel having relatively larger particle diameter can be made lower.
A predetermined distance is continuously required between the movable core and the first flange when the needle valve is seated on the seat portion, so as to raise the moving speed of the needle valve in the separating direction. The predetermined distance is maintained by the second elastic member located between the second flange and the sleeve, because the second elastic member presses the movable core onto the stopper, in JP-B2-4243610. If the needle valve and the movable core are configured not to have relative movement with each other, the second elastic member to press the movable core onto the stopper is unnecessary, because the first elastic member presses the needle valve in the seating direction. In contrast, in JP-B2-4243610, the second elastic member to press the movable core onto the stopper is necessary other than the first elastic member to press the needle valve in the seating direction, so as to raise the moving speed of the needle valve in the separating direction. However, the fuel injection valve has a complicated structure in this case.